During the past several years, environmental pollution concerns have led those active in the coatings, castings and moldings arts to develop various curable compositions in which organic solvents derived from petroleum have been eliminated or at least substantially minimized. Thus, compositions such as water-based compositions and high solids compositions have been extensively investigated. Even more recently the petroleum embargo and the resultant high cost and scarcity of petroleum by-products has engendered interest in the development of curable compositions which are composed entirely of, or at least substantially of, inorganic components.
The present invention relates to a curable composition composed essentially of inorganic constituents. More particularly, the present invention relates to curable compositions comprising aqueous solutions of water-soluble silicates and water-soluble borate latent insolubilizers, having dispersed therein an inorganic pigment, preferrably TiO.sub.2.
A number of water-soluble silicate compounds are known in the art. Such compounds include sodium silicate, potassium silicate, lithium silicate and quaternary ammonium silicates which readily dissolve in water to form solutions therewith. Inasmuch as the pH of these solutions is normally higher than about 10.5, the silica will remain soluble therein. However, when these water-soluble silicates are blended with insolubilizing agents (i.e., crosslinkers) quite often the resultant solution is unstable. Thus, for example, the combination of water-soluble silicates with metal oxides of the form M.sub.x O.sub.y such as cadmium oxide, copper oxide, calcium oxide, lead oxide and the like has produced unstable systems in that these materials ordinarily cause precipitation or gelation. In addition to problems of composition stability, compositions formed from water-soluble silicates and water-soluble insolubilizers have in the past proven to be extremely sensitive to water. Thus, such compositions have heretofore been deficient in web abrasion resistance.
Accordingly, a curable composition containing a water-soluble inorganic silicate and a water-soluble insolubilizer or crosslinker which produces products having excellent resistance to water as well as other desirable properties would be of considerable advantage.